1. Field of the Invention
The present invention relates to incandescent lights, and, more particularly, to adapters designed to improve their performance.
2. Background Information
Over the past 40 years, particularly since semiconductor devices have become readily available, there has been substantial activity (including patenting such devices) relating to adapters which can enhance or modify the performance of incandescent lights, which henceforth will be referred to collectively as lamps. Most of the prior art has related to adaptive devices which can be affixed to the external screw base of the lamps in either a removable or non removable way. U.S. Pat. Nos. 3,818,263 and 4,989,607 illustrate removable adapters, and U.S. Pat. No. 3,823,339 shows a permanent adapter. Some configurations have involved adaptations within the glass envelope itself prior to the screw base being attached, for example U.S. Pat. No. 4,480,212 describes such an assembly. Each of the foregoing U.S. Patents are hereby incorporated herein by reference.
Present in virtually all of the adaptive approaches is concern about filament-generated heat. Such heat can degrade performance of the semiconductors or other electronic components involved. Silicon semiconductor devices typically do not have ratings much over 150 degrees C. The presence of self-generated heat, along with a very high filament cause ambient temperature can be a destructive combination. U.S. Pat. No. 4,480,212 notes such heat considerations. This Patent is hereby incorporated herein by reference.
An earlier patent, U.S. Pat. No. 3,215,891, notes that silicon rectifiers have a relatively high temperature capability, typically to 150 degrees C. (Celsius), and, having a relatively simple device structure, do not exhibit the thermal runaway characteristics of semiconductors which either have multiple junctions or have properties which are very sensitive to thermal effects. This patent is hereby incorporated herein by reference. Consequently, it is feasible to place such device within the glass envelope of the lamp and still have them survive the high ambient temperature.
However, as adaptive techniques have evolved which employ multi-junction semiconductors, there tends to be more vulnerability to performance degradation at high temperatures. An article by the present inventor, E. Rodriguez, entitled, “Cooling a High Density DC-DC Converter Impacts Performance and Reliability” PCIM Magazine, November 1999 pp 60–66 describes in detail the principles of heat removal from a semiconductor chip and the subtleties of optimizing such heat removal paths. U.S. Pat. No. 6,515,858 further describes such heat removal principles and how the functional stability or failure susceptibility of any given semiconductor is a function of its closeness to its maximum operating temperature. This patent is hereby incorporated herein by reference.
It has been noted that it is the combination of ambient temperature with self-generated heat which is the destructive combination. In other words, a device might very well survive the high temperature within a lamp glass envelope but the self generated heat, if not removed, raises the junction temperature far above acceptable levels. Consequently, in prior art, it has generally not been possible to place within the glass envelope of a lamp any silicon semiconductors of a dissipative nature other than simple rectifier diodes. Non silicon, multi-junction semiconductors, employing materials such as gallium arsenide can withstand much higher temperatures, but the costs and performance limitations of such devices has precluded them from commercial lighting applications.
In a typical Edison base incandescent lamp, it is customary to have the filament enclosed with a sealed glass envelope, essentially evacuated of air and then filled with certain inert gases within that envelope to promote longer filament life. The design of the filament and the types of gases employed within the envelope are not particularly relevant to the proposed embodiment and will therefore be omitted from further description. Suffice it to say a wire is connected, within the sealed glass bulb envelope, to each end of the filament. In one small area of the glass envelope, through which the air is evacuated, the glass is essentially pinched and sealed by heating the glass in that area to the melting point in the manner noted in the bottom of a typical glass thermometer.
The two wires from the filament pass through that pinched and sealed glass area. This forms what is called a glass-to-metal seal in that no air or other gas can escape or pass through the same tiny hole through the wire passes. The two wires, now being outside of the sealed glass envelope, are directed to, and soldered or welded within, two holes in the screw base, one hole being in the center and one being on the periphery. The center connection will subsequently make contact with the center contact of a socket while the outer contact will make contact to the outer screw shell of a socket.
In a final configuration, having the screw base attached to the glass envelope, there is very little air space within the screw base in which to place any electronic device or circuit board.
Furthermore, because of the special shapes involved for the pinched and sealed glass area, as well as glass insulation cones within the screw base, there is a less than ideal environment in which to install an electronic circuit, aside from the need to address thermal considerations. It is therefore a principal objective of the proposed embodiment to make best use of the minimal space in a way which exhibits thermal advantages.
To those skilled in the art relative to power semiconductors and associated heat sinking or cooling considerations, it is known that cooling is very dependent on the metallic surface area to which a semiconductor chip is attached. Reference 1 describes in detail the concept of thermal resistance and the physics of such a concept need not be further described. Generally, it is known that the junction of a semiconductor will elevate in temperature in accordance with what is called its thermal resistance, specified in degrees C. per watt to the ambient air. That means, for example that the semiconductor will increase in temperature a predictable amount for every watt of power. The temperature rise will typically be cut in half for every quadrupling of the surface area to which the semiconductor chip is affixed in a thermal conductive manner.
When the semiconductor is in chip form (i.e. unpackaged) or is in a small surface mount package, It has very little surface area and its thermal resistance for example can be as high or higher than 200 degrees C. per watt. Therefore, it is imperative for a device handling any amount of power that the surface area, to be significantly more than the chip itself. Otherwise, the chip can handle almost no power—not because it can intrinsically carry little current but because it simply overheats.
For example, microprocessor chip in a computer by itself might handle only a small fraction of a watt, and therefore be rendered useless, but mounted properly onto a metallic thermally conductive surface of area much greater than the chip itself, can handle tens of watts. In the proposed embodiment therefore, it is the intent to define a configuration in which the mounting surface is substantially greater than the component itself. It is not the three dimensional shape of the mounting surface which is most important but rather the total surface area.